The present invention relates to novel well treatment fluids comprising improved additives. Particularly desirable are well treatment fluids having an improved biodegradability since a significant part of these fluids generally comes into contact with the environment.
The term “well treatment fluid” used herein includes, but is not limited to fluids used in the drilling of bore holes in rock to lubricate and cool drill bits, and to transport rock cuttings away from the rock face. The term includes “drilling fluids”, “spacer fluids” and “fracturing fluids”. Space fluids are used to clean the sides of bore holes prior to cementing. Drilling fluids are used in the construction of deep wells and bore holes, and especially oil and gas wells. During the drilling of oil and gas wells, drilling fluid is typically circulated in the well bore to cool and lubricate the drill bit and pipe, to carry cuttings from the bottom of the well bore to the surface, and to impose a hydrostatic head on the drilled formation to prevent the escape of oil, gas, or water from the well bore. Also, the term well treatment fluid as used herein embraces “completion muds” or “completion fluids”, which are preferably used in civil engineering and the construction industry to stabilize holes and excavations by preventing the breakdown of shales on exposure to water. The term well treatment fluid is also used herein to include “packing fluids” which are used in drilling operations to fill the space between concentric, downhole tubing used in the well casing. The term “well treatment fluid” also includes “drill-in” fluids and “workover fluids”. A “drill-in” fluid is generally a drilling fluid used to drill the well bore into producing portions of a subterranean formation so as to minimize damage, maximize production of exposed zones, and facilitate any necessary well completion needed. A drill-in fluid generally contains fewer solids than a drilling fluid, and what solids it does contain are often size controlled to minimize penetration or invasion into the formation matrix to avoid damaging the production formation. Preferably, the term “well treatment fluid” is a fluid selected from the group consisting of drilling fluid, drill-in fluid, completion fluid, fracturing fluid and workover fluid.
In addition, the well treatment fluid of the invention is useful as a spearhead fluid for the removal of unwanted deposits or hydrocarbons prior to the introduction of a stimulation (or other well treatment) fluid.
For various applications it is desirable to be able to adjust the viscosity of well treatment fluids. For this purpose viscosifier additives can be included. Also it may be necessary to add corrosion inhibitors to protect metal parts of machinery from corrosion if the parts come into contact with the well treatment fluids and/or with other fluids and gases from the well.
It is important that the additives used in well treatment fluids are ideally non-toxic or have only a low toxicity since as mentioned the well treatment fluids will be contact with the environment. For offshore drilling operations it is particularly advantageous if the well treatment fluids and additives therefore exhibit particularly low levels of toxicity towards marine microbial life forms also since these microorganisms enter into the food chain of larger life forms and are critical to maintain a stable ecosystem.
However, well treatment fluids for stimulation and remediation as well as fluids for removing drilling muds from the wellbore, for example prior to cementing or introduction of a completion brine, or for other purposes and additives therefore such as viscosifiers and corrosion inhibitors presently used are either not biodegradable or are less efficacious than required.
Thus, in particular for demanding applications there is a continued need for more effective well treatment fluids and additives therefore, which are at the same time characterized by a an improved biodegradability and low toxicity.
It was therefore an object of the invention to provide novel well treatment fluids and additives therefore which meet this demand.